Synthesis And Study On Functional Interlayers For Lithium-sulfur Batteries

Lithium-sulfur batteries are considered to be one of a new generation of energy storage devices,because of their high energy density and low cost.The theoretical capacity is up to 1675 mAh g-1 and energy density is 2600 wh kg-1,which is higher an order of magnitude than traditional lithium-ion batteries.In addition,sulfur has advantages of natural abundance,low cost and environmental friendliness.However,the elemental sulfur and discharge products are insulator.The intermediates are highly soluble in organic electrolyte and the electrode volume changes during cycling.All of these effects restrict the electrochemical performance of sulfur.In order to improve the specific capacity and cycling life of lithium-sulfur batteries,this paper is aimed at exploring the influence of different functional interlayer on the battery performance.The functional interlayer with high electronic conductivity and adsorption ability can improve the electrochemical performance of batteries.In this paper,we first used the self-supporting PANI-GO as a functional interlayer.By in-situ polymerization method,thin layer of conductive polymer PANI is grown on the surface of conductive basement GO.As we all known,PANI has chemical adsorption of lithium polysulfide,at the same time,the conductive interlayer can work as upper current collector to reactivate the sulfur on the surface of cathode.After 100 cycles,the morphology of the interlayer was characterized by SEM,and the cathode with PANI-GO interlayer showed porous structure and hardly found insoluble product deposited on the surface of cathode.For the cathode without interlayer,the particles aggregated and cracked seriously after 100 cycles.Compared to use the GO interlayer,the batteries with PANI-GO interlayer exhibited a high initial specific capacity of 1261 mAh·g-1 at a high current density of 0.2 C,and still maintained at 832.8 mAh·g-1 after 100 cycles,which have better stability and higher specific capacity.Based on the above experiments,we research the PANI-TiO₂ composite as interlayer.PANI-TiO₂ materials were coated to the commercial membrane with a simple technology.The cycle stability of the battery was apparently improved due to PANI-TiO₂ materials as coating layer,.By EDS analysis of the interlayer after 200 cycles,we found that the peak of elemental sulfur which confirmed that the PANITiO₂ coating layer effectively adsorbed lithium polysulfides.To further verify interlayer the influence on the performance of lithium-sulfur batteries,we use pure sulfur as cathode to improve the loading of sulfur electrode.After treated by concentrated sulfuric acid,the conductivity of CNT and conductive polymer PEDOT:PSS hybrid membrane was highly improved.PEDOT:PSS can restrict the polysulfide immigrating to lithium anode by the chemical absorption.In addition,the porous structure of the interlayer can store a part of polysulfides to improve the stability performance of Li-S batteries.Even if the cathode was pure sulfur,the Li-S batteries with PEDOT:PSS-CNT interlayer exhibited a high initial specific capacity of 921 mAh·g-1 at a high current density of 0.5 C,and still maintained at 653 mAh·g-1 after 200 cycles.The good stability and high specific capacity provided experimental and theoretical basis for the commercial application.